1. Technical Field
The present invention relates in general to improved performance for a disk drive actuator and, in particular, to an improved system, method, and apparatus for reducing off-track gain for the second primary resonance of a disk drive actuator in the off-track direction.
2. Description of the Related Art
Data access and storage systems generally comprise one or more storage devices that store data on magnetic or optical storage media. For example, a magnetic storage device is known as a direct access storage device (DASD) or a hard disk drive (HDD) and includes one or more disks and a disk controller to manage local operations concerning the disks. The hard disks themselves are usually made of aluminum alloy or a mixture of glass and ceramic, and are covered with a magnetic coating. Typically, one to five disks are stacked vertically on a common spindle that is turned by a disk drive motor at several thousand revolutions per minute (rpm). Hard disk drives have several different typical standard sizes or formats, including server, desktop, mobile (2.5 and 1.8 inches) and microdrive.
A typical HDD also uses an actuator assembly to move magnetic read/write heads to the desired location on the rotating disk so as to write information to or read data from that location. Within most HDDs, the magnetic read/write head is mounted on a slider. A slider generally serves to mechanically support the head and any electrical connections between the head and the rest of the disk drive system. The slider is aerodynamically shaped to glide over moving air in order to maintain a uniform distance from the surface of the rotating disk, thereby preventing the head from undesirably contacting the disk.
A slider is typically formed with an aerodynamic pattern of protrusions on its air bearing surface (ABS) that enables the slider to fly at a constant height close to the disk during operation of the disk drive. A slider is associated with each side of each disk and flies just over the disk's surface. Each slider is mounted on a suspension to form a head gimbal assembly (HGA). The HGA is then attached to a semi-rigid actuator arm that supports the entire head flying unit. Several semi-rigid arms may be combined to form a single movable unit having a rotary pivotal bearing system.
The head and arm assembly is pivotally moved utilizing a magnet/coil structure that is often called a voice coil motor (VCM). The stator of a VCM is mounted to a base plate or casting on which the spindle is also mounted. The base casting with its spindle, actuator VCM, and internal filtration system is then enclosed with a cover and seal assembly to ensure that no contaminants can enter and adversely affect the reliability of the slider flying over the disk. When current is fed to the motor, the VCM develops force or torque that is substantially proportional to the applied current. The arm acceleration is therefore substantially proportional to the magnitude of the current. As the read/write head approaches a desired track, a reverse polarity signal is applied to the actuator, causing the signal to act as a brake, and ideally causing the read/write head to stop and settle directly over the desired track.
The motor used to rotate the disk is typically a brushless DC motor. The disk is mounted and clamped to a hub of the motor. The hub provides a disk mounting surface and a means to attach an additional part or parts to clamp the disk to the hub. In most typical motor configurations of HDDs, the rotating part of the motor (the rotor) is attached to or is an integral part of the hub. The rotor includes a ring-shaped magnet with alternating north/south poles arranged radially and a ferrous metal backing. The magnet interacts with the motor's stator by means of magnetic forces. Magnetic fields and resulting magnetic forces are induced via the electric current in the coiled wire of the motor stator. The ferrous metal backing of the rotor acts as a magnetic return path. For smooth and proper operation of the motor, the rotor magnet magnetic pole pattern should not be substantially altered after it is magnetically charged during the motor's manufacturing process.
The storage capacity of HDD's continues to increase at a dramatic pace. Increasing the track density on the disk surface is a key method of achieving this, and it is expected that this trend will continue in the future. In order to support increases in track density, the mechanical bandwidth of the HDD's actuator system must be continually improved. This means that the inherent mechanical resonances present in actuator structures, which create off-track disturbances, must be continually increased in frequency, reduced in amplitude, or completely eliminated. There is a need for a solution that will reduce off-track gain for the second primary resonance of an HDD actuator in the off-track direction.
One of the key technologies commonly proposed for very high track density HDD's is the use of two-stage actuators. This technology splits the traditional single stage actuator in use today into two devices, one of which can be very small and light. The second stage of a two-stage actuator can achieve very high mechanical bandwidths, thereby supporting high track densities. Unfortunately, the implementation of two-stage actuators significantly increases system cost. The component count is typically more than doubled when two-stage actuators are used in disk drives. Moreover, the complexity of controlling a two-stage system increases significantly as well. This leads to reductions in system reliability and production yields. Thus, an improved solution that reduces off-track gain for the second primary resonance of an HDD actuator in the off-track direction is needed.